In recent years, a technology of iris recognition that performs personal authentication using a human's iris has been put into practical use. Since a fine pattern of an iris is used for iris recognition, a high resolution iris image is required in order to realize iris recognition that satisfies sufficient accuracy. The high resolution image refers to, for example, an image of around 400 pixels in the vertical direction and around 400 pixels in the horizontal direction for an iris of one of the eyes.
A conceivable method of obtaining a high resolution iris image may be to cause a camera having a proximity lens to come close to the eye and capture it. However, it is inconvenient to move the user's eye close to the camera or move the camera close to the user's eye every time performing iris recognition.
To improve convenience at the user, it is desirable to capture a high resolution iris image at a position distant from the user. When an iris is captured at a position distant from the user, there is difficulty due to an uncertain position of the user or individual differences of the heights or the like among users. Further, since there is a limit in increase of the resolution of a camera, it is difficult to capture, in a short time at a high resolution, the entire range where the user's iris may be located. Thus, there is a demand for a technology of acquiring a high resolution iris image at a position distant from the user.
The art disclosed in Patent Literature 1 first acquires a plurality of images including a wide range by using a wide angle camera and then determines the position of a human's eye from a connected image formed of a plurality of images. The art then performs capturing with a telescope camera being focused on the position of the eye and acquires an image including an iris. With such a configuration, even when there is a positional shift of a user or there are individual differences among users, a high resolution iris image can be acquired.
The art disclosed in Patent Literature 2 first acquires an image including a person by using two human-position cameras and then detects the position in the vertical direction of an iris from the image. Next, the art adjusts the angle in the vertical direction of a mirror provided on a light path of an iris camera to the position of the iris and then captures a plurality of images by using the iris camera while rotating the mirror in the horizontal direction. The art then selects an image including the iris out of the plurality of images. With such a configuration, even when there is a positional shift of a user or there are individual differences among users, a high resolution iris image can be acquired.